(1) Field of the Invention
The invention relates to a filter for fluids, in particular water,                comprising a filter surface and a rotary spray arm within the filter,        for conducting a flushing medium against the filter surface.        
The subject matter is primarily—but not exclusively—prescreens, which are arranged beneath a water surface on the suction side of a pump of a water intake.
(2) Prior Art
A filter of this type is disclosed in U.S. Pat. No. 6,508,933 B2. The filter consists of a cylindric side wall of plastic material closed at one side by a bottom, also of plastic material, and on the other side fully covered by a screen functioning as the filter surface. A spray arm equipped with nozzles is arranged in a rotary manner on a support centrally attached at the bottom of the filter. In the lower range of the filter, a tube provided with openings passes through the wall to the outside as an outlet for the water and is connected to the suction side of a pump. Pressurized water or pressurized air can be fed to the nozzles of the spray arm via a conduit, which passes through the side wall of the filter and through the support of the spray arm up to the latter. If the pump suction pressure is applied to the outlet tube, water from the surroundings is fed through the filter surface into the interior of the filter and from there, free of dirt is fed to the water system via the outlet and the pump. The filter surface is continuously cleaned of dirt deposited on the outside of the filter surface, by the rotary spray arm conducting flushing water or pressurized air fed via the pressured-water or pressurized-air conduit from the inside against the filter surface and thus removing the deposits.
The rotary movement is applied to the spray arm via an oblique position of the nozzles on the spray arm. By dividing the effect of the flushing medium for simultaneous use in driving and cleaning, the cleaning efficiency of the flushing medium jets is reduced. Moreover, by means of pressurized-water drive a rotary movement
of the spray arm is only possible in the same sense of rotation, and continuously. Also, the filter surface is comparatively small in relation to the volume and the structural size of the filter.